Chicago — Up and down the flood-ravaged river valleys of the upper Midwest, high water has inflicted billions of dollars of damage to homes, businesses, and crops. It has displaced tens of thousands of families and brought immeasurable suffering. It has also brought a new concern for the region’s river towns and cities: Flooding in the Midwest seems to be getting worse.

Researchers and other observers say such episodes are likely to worsen as efforts to protect vulnerable communities are outpaced by factors that increase the risk of flooding, including the ongoing practice of building on river flood plains.

Most cities and towns in the Midwest lie along rivers and streams. Hydrologists and planners say that the cumulative effects of decades of land-use choices have gradually increased the likelihood of flooding. Throughout Iowa, Illinois, and Indiana, for example, much farmland is drained by buried tiles that carry rainwater quickly away from the fields into streams and rivers. Population growth, bringing new highways and subdivisions, increases runoff. And communities keep building on flood plains, which not only puts new development at risk but also reduces the amount of flood plain available to absorb floodwater.

In many communities, levees protect low-lying neighborhoods and farmland. “America has had a love affair with levees since the 1800s,” says Marceto Garcia, professor of civil and environmental engineering at the University of Illinois at Champaign-Urbana. But levees cause new problems by confining rivers and increasing flooding in other stretches.

“The water has to go somewhere,” says Douglas Johnston, chairman of the community and regional planning department at Iowa State University in Ames. “It will go higher and faster downstream. Any defensive measure taken upstream will only heighten the problem downstream.”

Levees also leave some people with a false sense of security. In some cases, experts say, homeowners don’t know that their houses are at risk of flooding.

Experts also fault poor local planning. They say that economic and political pressures in many cases cause communities to slight flood-plain management for fear of hurting economic growth. In addition, they say, communities typically plan for present conditions without taking into account future growth and developments upstream that may create worse flooding – and worse damage – in the future.

“We have as a nation spent increasing amounts of money on preventing floods, and yet the cost of flooding continues to rise dramatically,” says Andrew Fahlund, vice president for conservation at American Rivers, an environmental advocacy group based in Washington. “Clearly we’re not doing something right. Certain kinds of flooding are going to be pretty much unavoidable. When water levels get to a certain point it’s pretty difficult to prevent damage. Our hearts go out to people who have been impacted by all this. The fact is that we have reduced the capacity our rivers have to absorb these floods significantly.”

Climate change has recently cast a new and disturbing uncertainty over flood-management questions by suggesting that history may be an unreliable guide to the future. Kenneth Potter, a civil and environmental engineer at the University of Wisconsin-Madison, says many scientists agree that climate change is likely to increase the occurrence and severity of storms as well as droughts, and thus increase the likelihood of flooding.

“The question is, are you going to face that once a century or once every 10 years?” he asks.

Ten months ago, Gays Mills, Wis., suffered what was then the biggest flood in memory. Then, a week and a half ago, monsoon-like rains lashed the region, and an even worse flood washed through town.

Now, as the mud dries and local businesses like Mickelson’s grocery store reopen, residents are feeling vulnerable.

“After last year, we all kind of relaxed,” says village president Larry McCarn. “We all figured it would be a while before it happened again. Now people are saying it could happen next week.”

After the last major Midwest flood in 1993, some lessons were learned, experts say. In Iowa, Johnston said, some communities raised their levees, which helped them survive this year’s flood.

Other lessons went unheeded. The Clinton administration commissioned a major study of the flooding that, among other things, recommended an overhaul of flood management and closer coordination of state, local, and national efforts. “In terms of national policy since 1993, there has not been significant change,” says Mr. Larson.